Bulk upload support from new TSV file format

[daniaki]

Context

It would be nice to add support for creating variants from a file containing het/hom depth information. However, this file may contain rows with the same variant ID so care must be taken to collapse rows with the same ID:

1. Merging het depths into an array of integers
2. Merging hom depths into an array of integers
3. Other fields?

Backend changes

• Adding het depth array field to the Variant model
• Adding hom depth array field to the Variant model
• Updating relevant JSON serialiser classes
• Updating relevant views to handle Variant model and serialiser changes
• A function to parse this file and create a list of variant objects to bulk create, or update if they already exist.
• Creating a new upload view class to accept this TSV file:
  • Return a JSON response giving feedback on how many new variants were created, existing variants were updated, or actionable feedback for errors if any
• Create a command line tool to ingest file instead of using the UI
  • Command line tool can request input to proceed with operation given information about number of variants that will be created or updated, or perform a dry run
• Unit tests

Frontend changes

• Creating a new upload Page component to accept this TSV file:
  • Display feedback on how many new variants were created, existing variants were updated, or actionable feedback for errors if any
  • Display json schema information describing the expected file format
• Create a new json-schema describing the expected file format